Apparatus for drying heat sensitive particulate material

ABSTRACT

A screw conveyor is rotatably supported in a longitudinal semicircular housing and has an inlet for receiving moisture containing heat sensitive particulate material to be dried and an outlet for discharging the dried particulate material. A shell is positioned around the lower portion of the housing and receives hot gas from a furnace through an inlet. The heat from the hot gas is transferred by conduction through the walls of the screw conveyor housing to the bed of loose particulate material to evaporate the moisture therein as the bed is moved through the housing by the rotating screw conveyor. The hot gas flows the length of the housing and passes from the shell into a gas plenum located adjacent the discharge end of the screw conveyor. Tempering air is introduced into the plenum and admixed with the hot gas to reduce the temperature thereof. The tempered gas passes from the plenum into a pair of gas ducts that extend parallel to the enclosed screw conveyor. The gas ducts have a plurality of branch conduits that open into the screw conveyor housing and control the volume rate of flow of tempered gas entering the enclosed screw conveyor. The tempered gas is intimately admixed with the loose bed of particulate material to thereby heat the particulate material by convection and evaporate the moisture remaining therein. The gas exits through a vertical outlet extending upwardly through the screw conveyor housing. Thus, the particulate material is first dried by conduction from the hot gas through the walls of the housing and then simultaneously by conduction and convection from the tempered gas introduced into intimate contact with the particulate material.

United States Patent 1 1 Davis 1 1 APPARATUS FOR DRYING HEAT SENSITIVE PARTICULATE MATERIAL David H. Davis, Fairmont, W. Va.

[73] Assignee: Consolidation Coal Company,

Pittsburgh, Pa.

[22] Filed: Aug. 26, 1974 [21] Appl. No.: 500,487

[75] inventor:

[52] US. Cl. 34/182; 34/166; 165/87;

165/92; 432/112 [51] Int. Cl. F26B 11/02 [58] Field of Search ..34/60, 130, 131, I42,

34/l39-l4l,166, 180-183; 165/87, 92; 241/57, 67, 113;432/3l, 112

Primary Examiner-Kenneth W. Sprague Assistant Examiner-James C. Yeung Attorney, Agent. or F1'rm-Stanely J. Price, Jr.; William A. Mikesell, Jr.

[57] ABSTRACT A screw conveyor is rotatably supported in a longitudinal semi-circular housing and has an inlet for receiv- [451 Sept. 16, 1975 ing moisture containing heat sensitive particulate material to be dried and an outlet for discharging the dried particulate material. A shell is positioned around the lower portion of the housing and receives hot gas from a furnace through an inlet. The heat from the hot gas is transferred by conduction through the walls of the screw conveyor housing to the bed of loose particulate material to evaporate the moisture therein as the bed is moved through the housing by the rotating screw conveyor. The hot gas flows the length of the housing and passes from the shell into a gas plenum located adjacent the discharge end of the screw conveyor. Tempering air is introduced into the plenum and admixed with the hot gas to reduce the temperature thereof. The tempered gas passes from the pienum into a pair of gas ducts that extend parallel to the enclosed screw conveyor. The gas ducts have a plurality of branch conduits that open into the screw conveyor housing and control the volume rate of flow of tempered gas entering the enclosed screw conveyor. The tempered gas is intimately admixed with the loose bed of particulate material to thereby heat the particulate material by convection and evaporate the moisture remaining therein. The gas exits through a vertical outlet extending upwardly through the screw con veyor housing. Thus, the particulate material is first dried by conduction from the hot gas through the walls of the housing and then simultaneously by conduction and convection from the tempered gas introduced into intimate contact with the particulate material.

7 Claims, 2 Drawing Figures APPARATUS FOR DRYING HEAT SENSITIVE PARTICULATE MATERIAL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to apparatus for drying moisture containing heat sensitive particulate material and more particularly to an enclosed screw conveyor mechanism for transporting the particulate material in a loose bed as it is dried by simultaneous conductive and convective heat transfer.

2. Description of the Prior Art Apparatus for drying moisture containing particulate material is well known in the art. U.S. Pat. No. 1,194,118 discloses a drying apparatus for drying grain, sand or other granular material, comprising a cylindrical vessel having an upper end portion into which is introduced the granular material. A helical conveyor positioned within the cylindrical vessel feeds the granular material downwardly. Hot gas is introduced into an axial conduit about which the helical conveyor is positioned. The hot gas transfers heat by conduction through the conduit to the granular material. The gas flows countercurrent to the direction of flow of the granular material and when it is discharged from the axial conduit it is introduced into a portion of the helical conveyor that is separated from the granular material. This provides further cocurrent drying by conduction.

In U.S. Pat. No. 1,322,428 gas is introduced at an elevated temperature into a cylindrical shell positioned about a vertical conveyor. The gas flows countercurrent to the direction of flow of the moisture laden material which is transported in liquid or semi-liquid form in the cylindrical conveyor. As the gasprogresses to the lower portion of the shell it is introduced through apertures into an inner cylindrical conveyor where the gas flows co-currently with the material. Thus, the material is dried by both conduction and convection. [n a similar arrangement, U.S. Pat. No. 1,510,693 discloses first the downward flow of hot gases with the pulverized fuel particles to dry the particles by convection. Thereafter, the hot gases flow upwardly through an axial conduit to further dry the particles by conduction.

In U.S. Pat. No. 2,627,668 apparatus for drying a fluidized mass of discrete particles, such as coal. ore concentrate and the like, is disclosed having a cylindrical enclosure in which gas is introduced and flows countercurrently to the flow of the particulate mass conveyed through the cylindrical vessel. A separate gas is introduced into a shell that extends around the external portion of the cylindrical enclosure to further treat the particles. In this manner the particles are dried simultaneously by both conduction and convection with separate gases used for convection and conduction.

In U.S. Pat. No. 2,639,681 there is disclosed a coal drying device in which the screw conveyor is divided into two sections. The first section has a shell therearound in which the coal particles are heated by conduction. The gas in the shell is conveyed into the second section of the screw conveyor onto the upper surface of the coal particles being conveyed through the second section where the coal particles are heated by convection.

There is a need for apparatus that dries moisture containing heat sensitive particulate material by the transfer of heat from a hot gas to the material by conduction and includes tempering the hot gas and controlling the flow of the tempered gas and thereby heat the material by convection to further evaporate the moisture as the material is being heated by conduction.

SUMMARY OF THE INVENTION In accordance with the present invention there is provided apparatus for drying moisture containing heat sensitive particulate material that includes an enclosed conveying mechanism for longitudinally conveying the particulate material in a loose bed. The enclosed conveying mechanism has an inlet for receiving the particulate material to be dried and an outlet for discharging the dried particulate material. A shell is positioned around the lower portion of the enclosed conveying mechansim adapted to receive and transport therethrough a gas at an elevated temperature. A gas inlet is connected to one end portion of the shell for directing the gas thereto. A gas tempering device communicates with the end portion of the shell. The temperature of the gas is reduced in the gas tempering device. A gas conduit system extending parallel to the enclosed conveying mechanism connects the gas tempering device with the enclosed conveying mechanism. The gas conduit system functions to convey the tempered gas into intimate contact with the moving bed of particulate material in the enclosed conveying mechanism. A gas outlet is provided in the enclosed conveying mechanism for discharging the tempered gas therefrom.

The enclosed conveying mechanism includes a longitudinal housing having aligned openings provided in the end portions thereof. A conventional screw type conveyor extends through the housing and is rotatably supported in the openings by bearings. The mass of moisture containing particulate material is fed through the inlet into the housing and is agitated by the rotating action of the screw conveyor which moves the particulate material in a loose bed longitudinally in the housing to the housing outlet.

A hot gas as from a furnace or combustion chamber is admitted through an inlet duct into the shell surrounding the conveyor housing. The heat is transferred from the hot gas through the walls of the housing to the bed of moving particulate material. In this fashion the moisture contained in the particulate meterial is evaporated by conductive heat transfer to thereby dry the particulate material. Thereafter, the hot gas enters the gas tempering device that communicates with the shell and is positioned at the discharge end of the enclosed conveying mechanism. The gas tempering device may include a gas plenum having means for reducing the temperature of the hot gases, such as by introducing air through an inlet in the gas plenum for admixture with the hot gas. By mixing the hot gas and air the gas is tempered to a suitable temperature so that when the tempered gas is conveyed from the gas plenum through the gas conduit system into the interior of the enclosed conveying mechanism the heat sensitive particles therein will be further dried by convective heat transfer without subjecting the heat sensitive particles to a drying gas above the temperature at which the particles will thermally decompose.

The gas conduit system includes a pair of conduits that extend parallel to the conveyor housing and are provided with a plurality of branch conduits that connect the gas conduits with the interior of the conveyor housing. In this manner the tempered gas is conveyed from the gas plenum through the gas ducts and branch conduits onto the upper surface of the particulate material moving through the housing by the action of the rotating screw conveyor. Each of the branch conduits includes a valve device for controlling the volume rate of flow of tempered gas that is directed into the enclosed conveying housing. In this manner the tempered gas is controllably introduced into contact with the loose moving bed of particulate material and intimately admixed therewith to heat the particulate material by convective heat transfer. Thus, additional moisture contained in the bed is evaporated and the drying of the particulate material is accomplished by direct and indirect drying through convection and conduction.

Accordingly, the principle object of the present invention is to provide drying apparatus to remove the moisture from heat sensitive particulate material by simultaneous conductive and convective heat transfer.

Another object of the present invention is to provide drying apparatus having a gas plenum in which the heating gas is tempered before the gas is brought into convective heat transfer relationship with the particulate material to be dried.

A further object of the present invention is to provide drying apparatus for removing the moisture contained in a filter cake or particulate material separated from a slurry in which the volume of hot gas brought into intimate contact with the material to be dried is selectively controlled by valve devices to thereby prevent thermal decomposition of the material.

A still further object of the present invention is to provide a heat drying apparatus for moisture containing heat sensitive particulate material that has been separated from a slurry and is to be dried by the combined effects of convection and conduction as it is longitudinally conveyed through a cylindrical housing in a loose bed by a screw type conveyor.

These and other objects of the present invention will be more completely described and disclosed in the following specification, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of the drying apparatus, illustrating the flow pattern of the hot gas to dry the particulate material as it is conveyed through the drying apparatus.

FIG. 2 is an end view of the drying apparatus. illustrating the connection of the outer shell and gas plenum for drying the particulate material by convection and the transfer of the hot gas into the gas ducts for drying the particulate matter by conduction.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings and particularly FIG. 1, there is illustrated apparatus for drying moisture containing heat sensitive particulate material generally designated by the numeral 10. For exemplary purposes, the drying apparatus is particularly suitable for drying heat sensitive particulate fuel. such as coal, that has been separated from a slurry in a slurry pond and for drying moisture containing filter cake and further for drying heat sensitive particulate material produced by vacuum filters and centrifugal dryers. The moisture containing particulate material. such as coal, is directed downwardly by gravity through a vertical inlet duct 12 of a conveying mechanisms generally designated by the numeral 14. The conveying mechanism 14 includes an enclosed longitudinal housing 16 having openings provided in the end portions thereof. A conventional screw type conveyor I8 is positioned in a trough like recess 20 of the housing 16.

The screw conveyor 18 is supported in the openings of the end portions of the housing 16 and includes a rotatable shaft 22 with end portions 24 suitably mounted in bearings 26. With this arrangement the wet particulate material enters the conveying mechanism housing 16 through the inlet duct 12 and is moved by the screw conveyor 18 from the inlet portion to the outlet portion of the housing 16. As the particulate material is moved longitudinally by rotation of the screw conveyor 18, the material, in a manner hereinafter described, is heated to evaporate the moisture contained therein without agglomerating the particles.

The agitation generated by the rotating screw conveyor 18 moves the wet particles in a loose bed from the inlet end portion to the discharge end portion of the conveying mechanism 14. At the discharge end portion the dried particulate matter exits the housing 16 through the vertical outlet duct 28 that is provided with an airlock 29. The dried particulate matter is then directed to a suitable conveyor for subsequent handling.

A semi-circular shell 30 having a tangentially positioned inlet duct 32 surrounds and is connected to the conveying mechanism recess 20. The opposite end portion of the shell 30 communicates with a gas tempering device such as a gas plenum. With this arrangement a gas at an elevated temperature, such as hot gas from a furnace or a combustion chamber, is tangentially introduced into the shell 30 surrounding the screw conveyor housing 16 through the inlet duct 32. The hot gas flows the length of the housing 16 and passes from the shell 30 into the gas plenum 34 at the discharge end portion of the conveying mechanism 14. Thus, the heat of the hot gas circulating through the shell 30 surrounding the housing 16 is transferred through the wall of the housing 16 by conduction to evaporate a a portion of the moisture contained within the mass of particulate material and partially dry the material. The drying operation is enhanced by the agitation of the particles by the screw conveyor 18 to bring the particles into contact with the heated walls of the housing 16 as the particles flow in a loose bed from the inlet portion to the discharge portion of the housing 16. The transfer of heat from the shell 30 to the particulate material within the housing 16 by conduction takes place along the entire length of the housing 16.

In the gas plenum 34 the temperature of the hot gas is reduced by a suitable manner, such as by admixing air introduced into the plenum 34 through the air inlet duct 36 with the hot gas. A damper device 38 is provided in the air inlet duct 36 and functions to regulate the volume of cooling air introduced into the gas plenum 34 and thereby control the process of reducing the temperature of the heating gas. In this manner the hot furnace gases are tempered within the gas plenum 34 as determined by the volume of air that is permitted to flow through the damper 38 positioned in the duct 36.

As illustrated in FIGS. 1 and 2, there is provided a pair of gas ducts 40 and 42 that extend parallel to the enclosed conveying mechanism 14. The gas ducts 40 and 42 communicate with the gas plenum 34 so that the tempered gas flowing from the gas plenum 34 enters the inlets ofthe gas ducts 40 and 42 through inlets 44. The end portions 46 of the gas ducts 40 and 42 are closed and a plurality of parallel spaced branch conduits 48 communicating with the gas ducts 40 and 42 extend into the conveying mechanism housing 16.

The tempered gas flows through the gas ducts 40 and 42 and is directed by the branch conduits 48 into the enclosed housing 16. Each of the branch couduits 48 are provided with a valve device 50, such as a butterfly valve, for controlling the volume rate of flow of tempered gas entering the housing 16. In this manner the volume rate of flow of the tempered gas entering the housing 16 can be regulated at preselected points along the length of the conveying mechanism 14.

The branch conduits 48 direct the flow of the tempered gas onto the upper surface of the loose bed of moving particulate material. The agitation of the particulate material generated by the screw conveyor 18 provides intimate admixing of the material with the tempered gas. Thus, the heat from the gas is transferred to the loose moving bed by convection to further dry the particulate material as it is conveyed from the inlet 12 to the outlet 28. Furthermore, the valve devices 50 by regulating the volume rate of flow of the tempered gas entering the housing 16 controls the rate of convective heat transfer to the particles. Thus, by tempering the hot gas and controlling the gas flow rate into the housing l6, the moisture on the particles is evaporated without excessively heating the particles which would result in thermal decomposition of the particles. The gas exits the conveying mechanism 14 through a vertical outlet duct 52 extending upwardly from the housing 16.

The heat supplied by convection to the moving bed of particulate material evaporates the moisture still remaining in the material and not evaporated by the conductive heating. Accordingly. when the material is discharged from the housing [6 through the outlet duct 28, the particles are substantially free of moisture. Thus, by the combined direct and indirect heating of the moving bed of loose particulate material through conduction and convection, the moisture contained in the particles introduced into the housing 16 through the inlet duct I2 is substantially removed when the particles are discharged from the housing 16 through the outlet duct 28.

According to the provisions of the patent statutes, l have explained the principle, preferred construction and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, it should be understood that, within the scope of the appended claims. the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. Apparatus for drying moisture containing particulate material comprising,

enclosed conveying means for longitudinally conveying the particulate material in a loose bed,

said enclosed conveying means having an inlet for receiving the particulate material to be dried and an outlet for discharging the dried particulate material,

a shell positioned around the lower portion of said conveying means for receiving a gas at an elevated temperature,

said shell arranged in heat transfer relation with a portion of the outer surface of said enclosed conveying means so that the heat from the gas is transferred by conduction through said enclosed conveying means to dry the particulate material therein,

a gas inlet connected to one end of said shell for directing the gas thereto,

gas tempering means communicating with said shell for reducing the temperature of the gas,

conduit means extending parallel to said enclosed conveying means and connecting said gas tempering means with said enclosed conveying means for conveying the tempered gas into intimate contact with the moving bed of particulate material in said enclosed conveying means, and thereby dry the particulate material by convection,

means for controlling the volume rate of flow of the tempered gas supplied through said conduit means into contact with the moving bed of particulate material in said enclosed conveying means, and

a gas outlet in said enclosed conveying means for discharging the tempered gas therefrom.

2. Apparatus for drying particulate material as set forth in claim 1 in which said conveying means includes,

an enclosed longitudinal housing having aligned openings provided in the end portions thereof, and

a screw type conveyor extending longitudinally through said housing and rotatably supported in said openings,

said screw type conveyor arranged to agitate and move particulate material in a loose bed from said inlet to said outlet.

3. Apparatus for drying particulate material as set forth in claim 1 in which said conduit means includes,

a pair of gas ducts extending parallel to said enclosed conveying means and communicating with said gas tempering means,

said gas ducts having a plurality of branch conduits that open into said conveying means to direct the tempered gas onto the upper surface of the particulate material within said enclosed conveying means.

4. Apparatus for drying particulate material as set forth in claim 3 which includes,

valve means provided in each of said branch conduits for controlling the volume rate of flow of tempered gas directed into said enclosed conveying means.

5. Apparatus for drying particulate material as set forth in claim 4 in which,

said valve means includes a plurality of butterfly valves operable to control and regulate the volume rate of flow of tempered gas entering said enclosed conveying means at preselected points along the length thereof.

6. Apparatus for drying particulate material as set forth in claim I in which said tempering means includes,

a gas plenum positioned adjacent to said outlet of said enclosed conveying means,

said gas plenum arranged in communication with said shell and conduit means to permit passage of the gas from said shell to said conduit means, and

said gas plenum having means for reducing the temperature ofthe gas prior to contacting said particulate material in said enclosed conveying means.

7 8 7. Apparatus for drying particulate material as set and forth clam 6 m wh'ch mcans for reducmg the said inlet having valve means for controlling the flow temperature of the gas includes.

said gas plenum having an inlet through which air passes into mixture with the gas to temper the gas.

of air into said gas plenum. 

1. Apparatus for drying moisture containing particulate material comprising, enclosed conveying means for longitudinally conveying the particulate material in a loose bed, said enclosed conveying means having an inlet for receiving the particulate material to be dried and an outlet for discharging the dried particulate material, a shell positioned around the lower portion of said conveying means for receiving a gas at an elevated temperature, said shell arranged in heat transfer relation with a portion of the outer surface of said enclosed conveying means so that the heat from the gas is transferred by conduction through said enclosed conveying means to dry the particulate material therein, a gas inlet connected to one end of said shell for directing the gas thereto, gas tempering means communicating with said shell for reducing the temperature of the gas, conduit means extending parallel to said enclosed conveying means and connecting said gas tempering means with said enclosed conveying means for conveying the tempered gas into intimate contact with the moving bed of particulate material in said enclosed conveying means, and thereby dry the particulatE material by convection, means for controlling the volume rate of flow of the tempered gas supplied through said conduit means into contact with the moving bed of particulate material in said enclosed conveying means, and a gas outlet in said enclosed conveying means for discharging the tempered gas therefrom.
 2. Apparatus for drying particulate material as set forth in claim 1 in which said conveying means includes, an enclosed longitudinal housing having aligned openings provided in the end portions thereof, and a screw type conveyor extending longitudinally through said housing and rotatably supported in said openings, said screw type conveyor arranged to agitate and move particulate material in a loose bed from said inlet to said outlet.
 3. Apparatus for drying particulate material as set forth in claim 1 in which said conduit means includes, a pair of gas ducts extending parallel to said enclosed conveying means and communicating with said gas tempering means, said gas ducts having a plurality of branch conduits that open into said conveying means to direct the tempered gas onto the upper surface of the particulate material within said enclosed conveying means.
 4. Apparatus for drying particulate material as set forth in claim 3 which includes, valve means provided in each of said branch conduits for controlling the volume rate of flow of tempered gas directed into said enclosed conveying means.
 5. Apparatus for drying particulate material as set forth in claim 4 in which, said valve means includes a plurality of butterfly valves operable to control and regulate the volume rate of flow of tempered gas entering said enclosed conveying means at preselected points along the length thereof.
 6. Apparatus for drying particulate material as set forth in claim 1 in which said tempering means includes, a gas plenum positioned adjacent to said outlet of said enclosed conveying means, said gas plenum arranged in communication with said shell and conduit means to permit passage of the gas from said shell to said conduit means, and said gas plenum having means for reducing the temperature of the gas prior to contacting said particulate material in said enclosed conveying means.
 7. Apparatus for drying particulate material as set forth in claim 6 in which said means for reducing the temperature of the gas includes, said gas plenum having an inlet through which air passes into mixture with the gas to temper the gas, and said inlet having valve means for controlling the flow of air into said gas plenum. 